New sources of protein concentrates are being sought to supplement the usual protein materials such as dry milk solids and soybean fractions. The concentration of the protein component in cereals and legumes is receiving much attention at the present time. These protein concentrates find use in diet supplements, bread and other bakery products, and other household foods as well as for industrial applications. The upgrading process usually consists of milling the cereal grain or oil seed to a sufficiently small size to liberate the protein component and separating that component from the other constituents. In one such method, the proteinaceous seed is ground to protein-liberating size (flour) and dispersed in a hydrocarbon solvent, e.g. hexane, where it is agitated to dissolve the oil and fat constituents. The slurry is then settled or centrifuged to separate the denser starch particles from the protein particles. With feed materials like oats and rapeseed, which require very fine grinding for separation, residual protein concentrates or fractions tend to remain in a stable suspension in the hexane-oil liquid, which suspension cannot be separated by centrifuging, filtration, or most other conventional means including hydrocyclones. Spray drying is possible, but it concentrates the vegetable oils and fats with the protein thereby lowering the protein ratio in the concentrate and making it undesirable for many end uses. The high stability of this liquid suspension is probably caused by naturally-occurring surface active agents, e.g. glycolipids and phospholipids peptizing the small proteinaceous particles.
In U.S. Pat. No. 4,154,728, May 15, 1979, R. W. Oughton, a process is described in which certain comminuted proteinaceous material is separated into fractions in the presence of an organic solvent, preferably by centrifugal means. The fractions have differing protein contents. This process is not very effective with oats or oilseed (e.g. rapeseed) solids, which contain considerable oil and require very fine grinding, and leave a very stable colloidal suspension of proteinaceous solids in the solvent.
In Canadian Pat. Nos. 1,082,174 of A. Bell, J. R. B. Boocock and R. W. Oughton, and 1,087,451 of R. W. Oughton similar processes for the separation of a variety of products from comminuted oats are disclosed. This organic solvent (hexane) process separates oats into three fractions: crude oat oil (and other extracted components); oat flour (mainly starch and protein); and oat bran (including some gums and trapped starch and protein). Again the residual solvent contains colloidal proteinaceous particles which have proved difficult to recover. If these solids are allowed to build-up on recycle of solvent, they will lead to high viscosity and other problems.
In some oilseed processing (e.g. rapeseed) where solvent (hexane) is used to contact solids, suspensions of proteinaceous solids may be formed which are difficult or costly to treat by conventional means.